The invention relates to a process for preparing an esterquat, compositions comprising said esterquat, and the use of said compositions as a gas hydrate growth inhibitor.
Gas hydrate crystals (clathrates of gases in a lattice consisting of water molecules) are formed in natural gas and crude oil by the interaction of low-boiling hydrocarbons, such as methane, ethane, propane, butane, and isobutane, and water under conditions of elevated pressure and reduced temperature. It has been known for a long time that gas hydrate crystals when allowed to form and grow inside a conduit such as a pipeline, tend to block or even damage the conduit. A number of methods have been suggested to prevent such blocking, of which the use of a crystal growth inhibitor is considered to be very attractive.
Various types of gas hydrate growth inhibitors are known in the art and at present preference is given to quaternary ammonium compounds (i.e. quats) due to their high efficiency. Preferred compounds contain at least one ester function in order to improve the biodegradability of the quat and such compounds are referred to as esterquats. A particularly interesting class of esterquat gas hydrate growth inhibitors are diesterquats.
WO 99/13197 relates to a method for inhibiting the plugging of a conduit by gas hydrates wherein use is made of a quaternary ammonium gas hydrate growth inhibitor. Diesters of dibutyl diisopropanol ammonium bromide and coconut fatty acid and of dibutyl diisobutanol ammonium bromide and coconut fatty acid are described. These diesterquats are prepared, e.g., by quaternizing dibutyl isopropanol amine with propylene oxide and hydrogen bromide in isopropanol, followed by acylation of the dibutyl diisopropanol ammonium bromide formed with coconut fatty anhydride.
Disadvantages of this process are that it proceeds in a low yield, that it requires the use of special equipment, that it uses a solvent, which needs to be removed, and that it uses coconut fatty anhydride, which is not readily available. A further drawback is that during the esterification one equivalent of coconut fatty acid is formed, which needs to be recycled. For these reasons, the process of WO 99/13197 is less attractive economically.
WO 96/34177 discloses the diester of dibutyl diethanol ammonium bromide and coconut fatty acid in Experiment A 2b and the diester of dibutyl diethanol ammonium chloride and tallow fatty acid in Experiment A 3b, but without giving experimental details on the preparation thereof (see page 6, lines 15-18 of WO 96/34177). These diesterquats are used for inhibiting the plugging of conduits by gas hydrates.
U.S. Pat. No. 5,523,433 discloses a process for preparing dialkyl diacyloxyalkyl ammonium compounds in which an alkyl dialkanol amine such as methyl diethanol amine is first esterified with a C12-C22 fatty acid in the presence of an acid having a pKa of below 5 such as hypophosphorous acid, followed by reaction with an alkylating agent such as methyl chloride in a solvent to form a diesterquat. It is further disclosed that such diesterquats are useful as fabric softeners.
It was found that the process disclosed in U.S. Pat. No. 5,523,433 works well for the synthesis of dimethyl diesterquats and trimethyl monoesterquats, but not for dialkyl diesterquats such as dibutyl diesterquats and trialkyl monoesterquats such as tributyl monoesterquats, containing C8-C30 fatty acyl groups which could only be obtained in relatively low yields. Another drawback is that a solvent is used.
EP-A-0 187 298 discloses a process wherein a trialkanol amine is esterified with an acid chloride and quaternized with a quaternizing agent. According to the description (page 4, lines 14-15), triethanol amine is the preferred tertiary amine. The length of the acyl group of the acid chloride is defined as from 2 to 10 carbon atoms in total, and Examples 1-3 and 4 describe the use of acetyl chloride and octanoyl chloride, respectively. It further discloses that the esterquats have surface-active properties and may be used as detergents. In Example 3 of this document it is described that solid n-butyl tris(2,3-di-hydroxypropyl)ammonium chloride, obtained by reacting bis(2,3-dihydroxypropyl)-n-butyl amine with 1-chloro-2,3-propanediol, was reacted with a 100% excess of acetyl chloride at reflux temperature for 5 hours to 95% completion. The reaction product was dried and subsequently crystallized from a mixture of organic solvents.
Just as U.S. Pat. No. 5,523,433, EP-A-0 187 298 does not relate to the preparation of esterquats in accordance with the present invention such as dibutyl diesterquats and tributyl monoesterquats containing C8-C30 fatty acyl groups either.
In view of the prior art discussed above, it was concluded that there is need in the art for an improved, economic route for synthesizing esterquats on a commercial scale.
The present invention is a process for preparing an esterquat composition comprising (a) reacting a tertiary amine according to formula l: 
wherein R1 represents a C3-C6 hydrocarbon group, R2 represents a C3-C6 hydrocarbon group, a xe2x80x94R4xe2x80x94OH group or a xe2x80x94CH2[CH(OH)]nCH2OR5 group, if R2 represents a C3-C6 hydrocarbon group, R3 represents a xe2x80x94R4xe2x80x94OH group or a xe2x80x94CH2[CH(OH)]nCH2OR5 group, if R2 represents a xe2x80x94R4xe2x80x94OH group, R3 represents a xe2x80x94R4xe2x80x94OH group or a xe2x80x94CH2[CH(OH)]nCH2OR5 group, if R2 represents a xe2x80x94CH2[CH(OH)]nCH2OR5 group, R3 represents a xe2x80x94CH2[CH(OH)]nCH2OR5 group, R4 represents a C2-C4 hydrocarbon group, n is 1-4, and R5 represents H or a C1-C30 hydrocarbon group, with a C3-C6 hydrocarbyl halide or a di(C3-C6) hydrocarbyl sulfate, followed by (b) reaction with a C8-C30 acid halide, with the proviso that at least one hydroxy group is esterified. Additionally, the invention includes compositions comprising this esterquat and the use of such compositions as a gas hydrate growth inhibitor.
As described above, esterquats may be used for inhibiting the plugging of conduits by gas hydrates. Compositions comprising said esterquats need to be transported and pumped through pipelines into the production lines near the gas or oil well. This requires a composition having a high active content with regard to the esterquat, which reduces transportation and storage costs, a low viscosity, which eases pumping, and a solidification temperature lower than xe2x88x9210xc2x0 C., which ensures handling of the esterquat composition in cold climate areas during winter time.
Surprisingly, a new and efficient process using readily available starting materials and standard production equipment and new esterquat compositions which meet the active content, viscosity, and solidification temperature requirements discussed above were found.
The process according to the present invention for preparing an esterquat composition comprises
(a) reacting a tertiary amine according to formula I: 
wherein
R1 represents a C3-C6 hydrocarbon group,
R2 represents a C3-C6 hydrocarbon group, a xe2x80x94R4xe2x80x94OH group or a xe2x80x94CH2[CH(OH)]nCH2OR5 group,
if R2 represents a C3-C6 hydrocarbon group, R3 represents a xe2x80x94R4xe2x80x94OH group or a xe2x80x94CH2[CH(OH)]nCH2OR5 group,
if R2 represents a xe2x80x94R4xe2x80x94OH group, R3 represents a xe2x80x94R4xe2x80x94OH group or a xe2x80x94CH2[CH(OH)]nCH2OR5 group,
if R2 represents a xe2x80x94CH2[CH(OH)]nCH2OR5 group, R3 represents a xe2x80x94CH2[CH(OH)]nCH2OR5 group,
R4 represents a C2-C4 hydrocarbon group,
n is 1-4, and
R5 represents H or a C1-C30 hydrocarbon group, with a C3-C6 hydrocarbyl halide or a di(C3-C6) hydrocarbyl sulfate, followed by
(b) reaction with a C8-C30 acid halide, with the proviso that at least one hydroxy group is esterified.
R1 may be a linear or branched C3-C6 hydrocarbon group. If R2 represents a C3-C6 hydrocarbon group, it may be a linear or branched C3-C6 hydrocarbon group.
R4 independently may be a linear or branched C2-C4 hydrocarbon group. R5 independently may be hydrogen or a linear or branched, saturated or unsaturated C1xe2x80x94C30 hydrocarbon group.
Preferably, R1 represents a C3-C6 hydrocarbon group and R2 and R3 both represent a xe2x80x94R4xe2x80x94OH group. More preferably, R1 represents a C4-C5 hydrocarbon group, most preferably an n-butyl group. Preferably, the tertiary amine is reacted with a C3-C6 hydrocarbyl halide, followed by reaction with a C8-C30, preferably C10-C24, more preferably C10-C18 acid halide.
Preferably, the C3-C6 hydrocarbyl halide is n-butyl bromide and the C8-C30 acid halide is cocoyl chloride.
The main product of the process according to the present invention is an esterquat according to formula II: 
wherein
R1 represents a C3-C6 hydrocarbon group,
R6 represents a C3-C6 hydrocarbon group, a xe2x80x94R4xe2x80x94Oxe2x80x94R9 group, or a xe2x80x94CH2[CH(OR10)]nCH2OR11 group,
if R6 represents a C3-C6 hydrocarbon group, R7 represents a xe2x80x94R4xe2x80x94Oxe2x80x94R9 group or a xe2x80x94CH2[CH(OR10)]nCH2OR11 group,
if R6 represents a xe2x80x94R4xe2x80x94Oxe2x80x94R9 group, R7 represents a xe2x80x94R4xe2x80x94Oxe2x80x94R9 group or a xe2x80x94CH2[CH(OR10)]nCH2OR11 group,
if R6 represents a xe2x80x94CH2[CH(OR10)]nCH2OR11 group, R7 represents a xe2x80x94CH2[CH(OR10)]nCH2OR11 group,
R4 represents a C2-C4 hydrocarbon group,
R9 represents H or a C8-C30 acyl group,
R10 represents H or a C8-C30 acyl group,
n is 1-4,
R11 represents H, a C1-C30 hydrocarbon group or a C8-C30 acyl group,
R8 represents a C3-C6 hydrocarbon group, and
Xxe2x88x92 represents a halide or a C3-C6 hydrocarbyl sulfate,
with the proviso that at least one ester group is present.
The main side-products of the process according to the present invention are C3-C6 ether derivatives and salts thereof formed by alkylation of one or more hydroxyl groups of the tertiary amine and tertiary amine salts formed from unreacted tertiary amine of formula I. As a result, C3-C6 ether derivatives of esterquats of formula II may also be formed.
R1 and R4 have the same meaning as described above. If R6 represents a C3-C6 hydrocarbon group, it may be a linear or branched C3-C6 hydrocarbon group. R8 may be a linear or branched, saturated or unsaturated C3-C6 hydrocarbon group. R9 and R10 independently may be hydrogen or a linear or branched, saturated or unsaturated C8-C30 acyl group. R11 independently may be hydrogen, a linear or branched, saturated or unsaturated C1-C30 hydrocarbon group or a linear or branched, saturated or unsaturated C8-C30 acyl group.
In a first preferred class of esterquat compounds according to formula II, R1 and R8 both represent a C3-C6 hydrocarbon group, R6 and R7 both represent a xe2x80x94R4xe2x80x94Oxe2x80x94R9 group, R4 represents a C2-C4 hydrocarbon group, R9 represents a C8-C30 acyl group, and Xxe2x88x92 represents a halide ion. These compounds are represented by formula III: 
Preferably, the sum of the number of carbon atoms present in the two R9 groups is from 20 to 36.
In a more preferred class of esterquats according to formula III, R4 represents a C2-C3 hydrocarbon group and R9 represents a C10-C24 acyl group, most preferably a C10-C18 acyl group.
In a second preferred class of esterquat compounds according to formula II, R1, R6, and R8 represent a C3-C6 hydrocarbon group and R7 represents a xe2x80x94R4xe2x80x94Oxe2x80x94R9 group, R4 represents a C2-C4 hydrocarbon group, R9 represents a C8-C30 acyl group, and Xxe2x88x92 represents a halide ion. These compounds are represented by formula IV: 
In a more preferred class of esterquats according to formula IV, R4 represents a C2-C3 hydrocarbon group and R9 represents a C12-C24 acyl group.
In a third preferred class of esterquat compounds according to formula II, R1, R6, and R8 represent a C3-C6 hydrocarbon group and R7 represents a CH2[CH(OR10)]nCH2OR11 group, R10 represents H or a C8-C30 acyl group, R11 represents H, a C1-C30 hydrocarbon group or a C8-C30 acyl group, n is 1-4, and Xxe2x88x92 represents a halide ion. At least one ester group should be present. These compounds are represented by formula V: 
When neither R10 nor R11 represent H, it is preferred that the sum of the number of carbon atoms present in R10 and R11 is from 20 to 36.
In a more preferred class of esterquats according to formula V, n is 1 and R10 and R11 both represent a C10-C24 acyl group, most preferably a C10-C18 acyl group.
In the structures of the esterquats according to formulae III-V, the C3-C6 hydrocarbon group preferably is a C4-C5 group, most preferably it represents an n-butyl group.
Either a single tertiary amine or a mixture of tertiary amines according to formula I may be used as the starting material in the invention process.
The invention process can be carried out using means and standard production equipment well-known to a person skilled in the art.
Step (a) of the invention process, i.e. the quaternization reaction, typically is carried out at a temperature of from 60xc2x0 C. to 120xc2x0 C. for a period of time of from 2 to 10 days.
It was found that with alkyl halides like butyl halides, the bromides gave a satisfactory selectivity and yield, whereas the corresponding chlorides gave a poor selectivity and low yield. For example, this was the case for the quaternization of N-n-butyl diisopropanol amine with n-butyl bromide as compared to quaternization with n-butyl chloride.
Further, it was observed that the selectivity to quats of the quaternization reaction is lower at higher temperatures, the main side-reaction being ether formation. The by-products formed are of the formulae I-II wherein one or more of the hydroxyl groups are transformed into C3-C6 hydrocarbyl ether groups. In addition, as a by-product the hydrogen halide or C3-C6 hydrocarbyl sulfuric acid salt of the tertiary amine starting material and/or ether derivatives thereof may be formed. So, it is preferred to determine the lowest temperature at which conversion takes place at an acceptable rate without causing solidification (see below) of the reaction mixture and to perform the reaction at that temperature. In general, the by-products need not be removed from the reaction mixture of step (a).
Preferably, use is made in the invention process of a C3-C6 hydrocarbyl halide. Most preferably, n-butyl bromide is used.
It is preferred to use an essentially stoichiometric amount of the C3-C6 hydrocarbyl halide. This yields optimum selectivity and reaction rate.
It further is preferred to carry out the quaternization reaction essentially in the absence of a solvent.
It was found that when carrying out the quaternization of N-n-butyl diisopropanol amine with an equimolar amount of n-butyl bromide in the absence of a solvent, some of the reaction product solidified during the reaction (at the reaction temperature). This solidification could be prevented by replacing at least 5 mole %, preferably 5-50 mole %, more preferably 5-20 mole %, of the amount of N-n-butyl diisopropanol amine with N-n-butyl diethanol amine. Solidification can also be prevented by replacing at least 10 mole %, more preferably 10-40 mole %, of the amount of N-n-butyl diisopropanol amine with N-n-butyl isopropanol ethanol amine as the starting tertiary amine. The person skilled in the art will recognize that these measures may also be applied to other tertiary amine starting materials in case solidification of the reaction mixture occurs.
Typical examples of suitable tertiary amines include N-n-butyl diethanol amine, N-n-butyl diisopropanol amine, N-n-butyl ethanol isopropanol amine, N-n-butyl ethanol sec-butanol amine, di-N-n-butyl 2,3-dihydroxypropyl amine, N-n-pentyl diisopropanol amine, N-n-pentyl diethanol amine, tertiary amines of the formula Bu2NCH2CH(OH)CH2OR5, wherein R5 represents a C1-C30 hydrocarbon group, (Bu)(HOCH2CH2)NCH2CH(OH)CH2OR5, wherein R5 represents H or a C1-C30 hydrocarbon group, and mixtures thereof. Preferably, the tertiary amine comprises N-n-butyl diisopropanol amine.
Typical examples of suitable C3-C6 hydrocarbyl halides include n-butyl bromide, n-pentyl bromide, allyl chloride, and mixtures thereof.
A typical example of a suitable di(C3-C6) hydrocarbyl sulfate is di-n-butyl sulfate.
Methods for preparing symmetrical and unsymmatrical dialkyl sulfates are known to the person skilled in the art, e.g., see Organic Syntheses, Collective Volume 2, John Wiley and Sons, Inc., New York, pages 111-112, Ullman""s Encyclopedia of Industrial Chemistry, Fifth Edition, Volume A8, VCH, Dialkyl sulfates and alkylsulfuric acids, K. Weisenberger and D. Mayer, pages 493-503, and DE 1200290.
The product of step (a) of the invention process can be used in step (b) with or without purification. If desired, the intermediate product may be (re)crystallized from a suitable solvent such as acetone, 2-butanone, and 4-methyl-2-pentanone. Preferably, no purification of the intermediate quaternary ammonium product is carried out.
Step (b) of the invention process, i.e. the esterification reaction, is carried out by contacting the reaction product of step (a) with a C8-C30 acid halide. Typically, step (b) is carried out in the absence of a solvent or a scavenger. A scavenger, in the form of an amine, typically is used in the art to capture the hydrogen halide formed during esterification.
In a typical reaction, the acid halide, normally an acid chloride, is dosed at such a rate that the evolution of acid, typically hydrochloric acid, is controlled. Typically, the esterification is carried out at a temperature of 20 to 110xc2x0 C. for a period of time of 0.5 to 5 h. For example, for the esterification of a mixture of di-n-butyl diisopropanol ammonium bromide and di-n-butyl diethanol ammonium bromide with cocoyl chloride the esterification temperature is kept between 95 and 100xc2x0 C. for about 2 h. The hydrochloric acid which evolves from the reaction mixture preferably is captured in a caustic scrubber.
It was found that the esterification products containing residual hydrogen halide remained pourable down to ambient temperature and did not require dilution with a solvent. As a result, the esterification in accordance with the present invention can be carried out with a highly efficient use of the reactor volume (i.e. a high space-time yield), leading to an economic process.
The C8-C30 acid halide preferably is derived from a readily available fatty acid, such as coconut fatty acid and tallow fatty acid, with coconut fatty acid being most preferred, using methods that are known to one of ordinary skill in the art.
The acid remaining in the reaction product of step (b) of the invention process preferably is neutralized, because it causes hydrolysis of the ester groups and corrosion of the equipment used. As is known to the person skilled in the art, this can be achieved in a number of ways. For example, use can be made of an organic base such as an amine, an inorganic base such as an alkali metal hydroxide or of a basic ion-exchange resin. Neutralization can be carried out after completion of or even during the esterification reaction as described below.
In one embodiment for carrying out the neutralization, the esterification reaction is run to completion and then the reaction mixture is diluted with a water-immiscible liquid which is a solvent for the esterquat and which allows phase separation. This solution is contacted with an aqueous solution containing 5-50 wt %, preferably 5-25 wt %, of an alkali metal hydroxide at a temperature of 10-90xc2x0 C., keeping a pH of 1-10, followed by separating the organic phase and, if desired, isolating the neutralized esterquat. Any amine salts formed during step (a) of the invention process (see above) are simultaneously converted into the corresponding free amines.
Preferably, for the neutralization an aqueous sodium hydroxide, i.e. caustic, solution is used.
Suitable water-immiscible solvents include aliphatic and aromatic hydrocarbons, ethers, and ketones. Typical examples include toluene, cumene, Shellsoll(copyright) AB, Shellsoll(copyright) N, Solvesso(copyright) 150, Solvesso(copyright) 200, Kemelix(copyright) 610, 4-methyl-2-pentanone, 2,6-dimethyl-4-heptanone, and cyclohexanone. Of these, ketones like 4-methyl-2-pentanone, 2,6-dimethyl-4-heptanone, and cyclohexanone are preferred.
The use of ketone solvents not only leads to an optimum result in the neutralization procedure, but the product solution obtained after neutralization also meets the various requirements set for formulations which are to be stored, transported, and used for inhibiting the growth of gas hydrates, notably with regard to cost of the formulation, safety (e.g. flash point), product solubility (e.g. solidification temperature), ease of transportation (e.g. viscosity), cost of transportation, storage stability, and ecotoxicity.
Preferably, in this embodiment of the neutralization a heel of an alkali metal salt solution, e.g., an aqueous sodium chloride solution, is provided, and then the organic phase (with the water-immiscible solvent) and the aqueous alkali metal hydroxide solution are added to the heel simultaneously. During neutralization the pH preferably is kept between 3 and 6, more preferably 3 and 5, in order to prevent ester hydrolysis, and the flows of the organic phase and the alkali metal hydroxide solution are adjusted accordingly. Below 50-60xc2x0 C. emulsification of the reaction mixture may occur, hence the temperature at which neutralization is carried out preferably is kept at 60-80xc2x0 C. Higher temperatures may cause too much hydrolysis of the ester groups.
The neutralization procedure can be carried out batchwise or continuously. It was found that neutralization could be carried out continuously either in one stirred tank or in two stirred tanks connected in series (see Examples).
In another embodiment of the neutralization procedure, the acid is neutralized by the addition of a sufficient amount of an organic base in the form of an amine, preferably a tertiary amine. As a result, the salt of the amine added is formed. The ratio between the (tertiary) amine added and the esterquat according to formula II can be controlled by evaporation of the acid, e.g., stripping of hydrochloric acid, from the crude reaction mixture.
In this embodiment, the amine can be added after completion of the esterification reaction or even during the esterification reaction. Preferably, it is added after completion of the esterification reaction. In this case, the amine may be added as such, e.g. ammonia, or in the form of an aqueous solution thereof, e.g. an aqueous ammonium hydroxide solution.
If desired, a small amount of a solvent, typically in an amount of 10 to 20 wt % based on the total weight of the mixture, can be used in order to improve the handling of the reaction product. The solvent can be added before or after neutralization with the amine. Any solvent may be used for this purpose.
Suitable solvents include the water-immiscible solvents that are mentioned above.
The tertiary amine preferably contains at least two C3-C6 hydrocarbon groups, at least two C3-C6 hydroxy-containing hydrocarbon groups or at least one C3-C6 hydrocarbon group and one C3-C6 hydroxy-containing hydrocarbon group. The third group on the tertiary amine may be a C1-C30 hydrocarbon group, optionally containing a hydroxy or ester group.
Typical examples of suitable tertiary amines include tri-n-butyl amine, di-n-butyl coco amine, and di(2-hydroxybutyl) coco amine.
This particular embodiment has the advantage that no waste water is generated and that the use of a solvent can be avoided. Moreover, it was found that salts of tertiary amines like tri-n-butyl amine and di-n-butyl decyl amine as such inhibited the growth of gas hydrates (see U. C. Klomp, V. Kruka, and R. Reijnhart, Low-dosage inhibitors: (how) do they work?, Proceedings of IBC Conference Controlling Hydrates, Waxes, and Asphaltenes, 20-21 October 1998, Aberdeen).
The present invention further relates to a composition comprising one or more esterquats of formula II as defined above, obtained by the process described above, and a ketone solvent as defined above.
The present invention also relates to a composition comprising one or more esterquats of formula 11 as defined above, obtained by the process described above, an amine salt, preferably a tertiary amine salt, as defined above and optionally a solvent as defined above.
Preferably, the compositions in accordance with the present invention comprise at least 30 wt %, more preferably at least 50 wt %, most preferably at least 70 wt %, of the esterquat, based on the total weight of the composition.
In a preferred embodiment of the compositions in accordance with the present invention, the composition further comprises 0.01-10 wt %, preferably 0.1-5 wt %, more preferably 1-3 wt %, of water, which acts as a co-solvent, based on the total weight of the composition, i.e. the organic phase. This amount of water may already be present after having carried out the neutralization procedure, or if it is not present in a sufficient amount, it may be added afterwards.
It was found that the presence of water provided a formulation having a reduced viscosity as well as a reduced solidification temperature while still providing a good hydrolytic stability of the esterquat. The presence of 1-3 wt % of water can compensate for about 10 wt % of solvent with respect to the viscosity of the formulation. This effect is even more pronounced with respect to the solidification temperature. This allows the production of formulations of a certain viscosity having a higher esterquat active content than formulations which do not contain a water co-solvent. Being able to manufacture high active content formulations reduces costs with respect to the amount of solvent to be used, storage, and transport.
The present invention also relates to the use of the compositions described above for gas hydrate growth inhibition.